Triaxial Discrete Element Simulation of Soil-Rock Mixture with Different Rock Particle Shapes under Rigid and Flexible Loading Modes

Three-dimensional scanning technology was used to construct the database of natural block stone shapes with different particle sizes. On the basis of Particle Flow Code 3D, a discrete element random model of soil-rock mixtures with different stone contents and shapes was established. A flexible boundary loading method of multisection wall was adopted to simulate the flexible film constraint mode of indoor triaxial test. Large-scale triaxial numerical simulation tests were carried out on the soil-rock mixture with different stone contents, stone shapes, and loading modes to analyze the macromechanics, microscopic deformation, and failure laws under various working conditions. Results showed that under the flexible loading mode, the stress curve of the samples with low stone content (0%-20%) has no obvious peak value and the deformation is mainly shear shrinkage. The stress curve of the samples with high stone content (40%-60%) showed the obvious peak value, and the dilatancy was prominent. Under the action of vertical load, the specimen bulged and formed multiple fork shear bands. Compared with the flexible loading mode, the rigid loading mode showed that the strength of the specimen increased in the rigid loading mode, and the cohesion and internal friction angle improved overall, but the friction energy was basically the same. During shearing, no obvious bulging was noted at the edge of the sample, and the shear bands were K-shaped and diagonal. The shape of block stone had significant influence on the strength, friction energy, and shear band shape of the soil-rock mixture.